Catalysts are used to improve the yield of saleable hydrocarbon products from thermal cracking of heavy oil, such as bitumen. The catalyst typically may consist of molybdenum or tungsten alone or combined with nickel or cobalt, carried on an alumina support. In the case of bitumen, both thermal cracking and hydrogen addition facilitated by the above catalysts are used in the upgrading process.
One of the major problems in such catalytic hydrocracking of heavy oil is the eventual loss of catalytic activity due to the deposition of metals and coke on the catalyst and catalyst support. Deactivation of the catalyst in this way requires that the catalyst be replaced or regenerated.
As a result, in recent years research has been carried out to develop an alternative to supported catalysts. One promising alternative is what can be called in situ-generated disposable catalysts. An oil-soluble transition metal compound catalyst precursor, such as molybdenum naphthenate, is distributed in the oil and heated to hydrocracking temperature. The precursor decomposes and reacts with sulfur moieties in the oil to form minute catalytic particles, such as molybdenum sulfide. Such small quantities of the catalyst (for example 100 ppm) are effective that single pass use is justified--hence the terminology "disposable".
To be effective in minimizing coke formation and maximizing liquid product yields, it has been shown that the in situ-generated catalytic particles need to be minute in size, typically less than 10 microns average mean diameter, thereby having a high surface area; they also need to be well distributed in the viscous oil.
Creating such catalytic particles which are minute in size and which are well distributed in the viscous oil has not been found easy to do. U.S. Pat. No. 5,578,197, issued to Cyr et al., discloses a technique involving dissolving molybdenum naphthenate precursor in the oil to be hydrocracked and distributing it therein by prolonged mixing at a mild temperature (selected so that the viscosity of the oil is reduced but decomposition of the precursor is avoided). Then the mixture is introduced to the hydrocracking reactor and the precursor decomposes and reacts with sulfur moieties in the oil to form the catalyst, when exposed to hydrocracking temperature. However, even though this technique has utility, the use of molybdenum naphthenate as the catalyst precursor is expensive.
An inexpensive source of molybdenum is the salt, ammonium heptamolybdate (hereinafter referred to as "AHM"). AHM is readily available in a coarse crystalline form.
However AHM, while water-soluble, is not oil-soluble; therefore it is not amenable to the technique disclosed in the Cyr et al. patent.
The work underlying the present invention has therefore been focussed on developing a process for using AHM as the catalyst precursor and dispersing it as very fine catalytic particles distributed in the heavy oil medium. However, it is contemplated that the dispersion process can also be applied to other transition metals as well.
For purposes of this application, the term "catalytic particle" is intended to cover both an in situ-generated catalyst precursor particle and the catalytically active particle produced from it. In the case of AHM, the term "catalytic particle" is intended to encompass one or more of: ammonium heptamolybdate, molybdenum oxides precursor particles derived from ammonium heptamolybdate, a mixture of molybdenum oxide precursor particles and molybdenum sulfide catalyst particles, and molybdenum sulfide catalyst particles.